\documentclass{article}

\begin{document}

\section{Common Messages}

ok

A positive response to another mensage, may include a
return value.

\begin{itemize}
\item Return Value
\end{itemize}

error

An error message.

\begin{itemize}
\item Message
\end{itemize}

\section{Authentication Server}
\subsection{Messages}

verify

Verify if a user exist, will return "ok" is the user
exist, error otherwise.

\begin{itemize}
\item Username
\end{itemize}

auth

Will authenticate a given user, will return ok if the
user and password are right, error otherwise.

\begin{itemize}
\item Username
\item Password
\end{itemize}

\section{Mailbox Server}
\subsection{Messages}

listmail

Will return a list of emails for a given user.

\begin{itemize}
\item username
\end{itemize}

mailinfo

\begin{itemize}
\item Number
\item Size
\end{itemize}

sendmail
\begin{itemize}
\item To
\item Recipent
\item Data Length
\end{itemize}

\end{document}
